Paste a domain. We auto-scan about 25 common ESP selectors in parallel (Google Workspace, Microsoft 365, Mailchimp, SendGrid, Mailgun, Postmark, Klaviyo, HubSpot, Zendesk, Salesforce). For each one we find, we decode the public key and tell you which keys are strong, weak, or in test mode. If you know your selector, paste it in for a direct lookup.